The present invention relates to a directional fluid control valve and more particularly, but not exclusively, to a high pressure valve of this kind for use in the oil, gas and petrochemical industries.
Directional fluid control valves typically comprise a valve body having a plurality of ports that provide communication between internal flow passages and external flow paths to or from other components. One or more valve members are moveable within the valve body between different switching positions to open or close the flow passages selectively and control the flow direction between ports.
Such valves are typically characterised by the number of ports (“ways”) and the number of discrete switching positions they provide. One example of a simple, common directional control valve is a two-position, two-way fluid control valve that provides selective communication between inlet and outlet ports. In such a valve, the valve member is biased by a spring into a first position in which it is either open or closed and an actuating force is applied by an actuator to overcome the spring force so as to move the valve member to the second position. However, the applied force must also be sufficient to overcome any imbalance in fluid pressure acting on the valve member and therefore the magnitude is related to the working fluid pressure of the control valve. In applications where there are high working fluid pressures, e.g., in pipelines for transporting fluid such as oil or gas at high pressures undersea or otherwise, the forces required to actuate the valve may be very large and even heavy duty solenoids actuators are not sufficient to operate the valve. In such applications there is a tendency therefore to use rotary ball valves. These can be used to allow for safe isolation of parts of the pipeline from fluid flow for the purposes of, for example, repair or maintenance. Such valves comprise a housing with an inlet and an outlet aligned for connection into the pipeline and a valve element in the form of a ball that is penetrated by a bore. The ball is disposed between the inlet and outlet and is rotatable relative to valve seats. Selective rotation of the ball brings the bore into and out of register with the inlet and outlet so as to permit or prevent flow between them. Actuation of the ball valve may be effected in several ways. For example it may be operated by a dedicated actuator (e.g. a pneumatically operated piston and cylinder) that is remotely operated. Alternatively, it may be operated manually by divers or by using a ROV.
The fluid flowing through such valves will often contain contaminants such as small particles of dirt etc. Such contaminants have a tendency to cause wear in rotary ball valves. In particular, as the ball rotates over the valve seat the contaminants can cause wear in the seat. Rotary ball valves thus have a limited number of valve operations before the valve seat deteriorates and internal leakage occurs.
At very high pressures the torque required to operate a rotary ball valve can be excessive.
There is a desire for a simple, inexpensive, yet robust valve in which the actuation force is reduced in comparison to traditional valve mechanisms.